gms 8.0 tutorial modflow – regional to local model...

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GMS 8.0 Tutorial MODFLOW – Regional to Local Model Conversion, Steady State Create a local model from a regional model using convenient tools provided in GMS

Objectives Use the convenient tools provided in GMS to perform the steps involved in a typical regional to local model conversion. This tutorial uses a steady state model. A transient example is provided in the MODFLOW – Regional to Local Model Conversion, Transient tutorial.

Prerequisite Tutorials • None

Required Components • Grid • Geostatistics • Map • MODFLOW

Time • 30-60 minutes

v. 8.0

1 Contents

1 Contents ...............................................................................................................................2 2 Introduction.........................................................................................................................2

2.1 Outline..........................................................................................................................3 3 Description of Problem.......................................................................................................3 4 Getting Started ....................................................................................................................4 5 Reading in the Regional Model..........................................................................................5 6 Converting the Layer Data to a Scatter Point Set............................................................5 7 Approach to Building the Local Model.............................................................................6 8 Building the Local Conceptual Model...............................................................................6

8.1 Creating a New Coverage ............................................................................................6 8.2 Creating the Boundary Arcs.........................................................................................7 8.3 Building the Polygon ...................................................................................................7 8.4 Marking the Specified Head Arcs ................................................................................8

9 Creating the Local MODFLOW Model............................................................................8 9.1 Creating the Grid..........................................................................................................9 9.2 Activating the Cells......................................................................................................9 9.3 Mapping the Properties ................................................................................................9

10 Interpolating the Layer Data ...........................................................................................10 11 Saving and Running the Local Model .............................................................................10 12 MODAEM Regional Model..............................................................................................10

12.1 Running MODAEM...................................................................................................11 12.2 Adjusting the Coverage Setup....................................................................................11 12.3 Running the Local Model...........................................................................................11

13 Conclusion .........................................................................................................................12

2 Introduction For many modeling studies, determining an appropriate set of boundary conditions can be difficult. It is often the case that classical boundaries such as rock outcroppings, rivers, lakes, and groundwater divides, may be located at a great distance from the site of interest. In such cases, it is often convenient to perform the modeling study in two phases. In the first phase, a large, regional scale model is constructed and the model is extended to well-defined boundaries. During the second stage, a second, smaller, local scale model is constructed that occupies a small area within the regional model. The groundwater elevations computed from the regional model are applied as specified head boundary conditions to the local scale model. The layer data, including elevations and transmissivities, are also interpolated from the regional to the local model. A more detailed representation of the local flow conditions, including low capacity wells and barriers not included in the regional flow model can be constructed in the local scale model. Regional to local model conversion is often referred to as “telescopic grid refinement."

GMS provides a convenient set of tools that can be used for regional to local model conversion. The steps involved in a typical regional to local model conversion using MODFLOW are described in this tutorial.

Page 2 of 12 © Aquaveo 2011

GMS Tutorials MODFLOW – Regional to Local Model Conversion, Steady State

2.1 Outline This is what you will do:

1. Open a regional conceptual model.

2. Convert the layer data to a scatter point set.

3. Build a local conceptual model and map to a 3D grid.

4. Map the conceptual model to a MODFLOW simulation.

5. Interpolate the layer data.

6. Run MODFLOW.

7. Run MODAEM.

8. Using the MODAEM head instead of the specified head, rerun MODFLOW.

3 Description of Problem The site we will be modeling in this tutorial is shown in Figure 1. The main features of the regional model are shown. Most of the boundaries are no-flow boundaries corresponding to groundwater flow divides, bedrock outcroppings, and natural flow boundaries. A river runs through the left side of the model. The narrow regions where the river enters and exits the model are modeled as specified head boundaries. There are four major production wells in the region. The site will be modeled using two layers: a lower confined layer and an upper unconfined layer.

The local site is situated in the interior of the model. The local site corresponds to a chemical plant with a small spill. Once the regional model is completed, a local scale model is to be developed and then used to analyze a number of injection/extraction well placement scenarios. The wells are part of a treatment system that is being designed.



Wells

Local Site Boundary

River

FixedHead

Boundary

FixedHead

Boundary

Figure 1. Regional model.

The basic goal of the regional to local model conversion process is to create a 2D scatter point set containing the heads and layer data arrays from the regional model, create the local model, and interpolate the heads and layer data to the local model. A 2D scatter point set is used since the MODFLOW arrays should be interpolated on a layer by layer basis using 2D interpolation. GMS provides a set of tools that greatly simplify this process. The basic steps are as follows:

1. Generate the regional model and compute a solution.

2. Use the MODFLOW Layers 2D Scatter Points command to create the scatter point set with the layer and head data from the regional model.

3. Create the 3D grid for the local scale model.

4. Interpolate the heads and layer data values from the scatter points to the MODFLOW layer arrays for the local scale model.

Each of these steps will be described in more detail below.

4 Getting Started Let’s get started.

1. If necessary, launch GMS. If GMS is already running, select the File | New command to ensure that the program settings are restored to their default state.



5 Reading in the Regional Model The first step in the model conversion process is to build a regional model. Since the focus of this tutorial is primarily on the conversion process, we will read in a previously constructed model.

1. Select the Open button .

2. Locate and open the file entitled tutfiles\MODFLOW\reg2loc_ss\regmod.gpr.

We are now viewing the top layer of the two layer model. You may wish to use the arrow buttons in the Tool Palette to view the bottom layer. The wells are located in the bottom layer. When you are finished, return to the top layer.

This model was constructed using the conceptual model approach. The boundary of the local site is indicated with a red rectangle. The conceptual model consists of three coverages. The coverage we are viewing is for the sources and sinks. There is also a coverage defining recharge zones and a coverage defining hydraulic conductivity zones for the top layer.

The project we imported includes the solution for the regional model. You should see contours of computed head.

6 Converting the Layer Data to a Scatter Point Set The first step in converting the regional model to a local model is to convert the MODFLOW layer data to a 2D scatter point set.

1. Select the 3D Grid Data folder in the Project Explorer.

2. Select the Grid | MODFLOW Layers 2D Scatter Points command.

3. Change the scatter point set name to Regional Data.

4. Turn on the following options:

• Layer elevations

• Computed heads

5. Click the Select Data Set button.

6. In the Select Data Set dialog, select the Head data set under the regmod (MODFLOW) solution and click OK.

7. Select the OK button to exit the MODFLOW Layers -> Scatter Points dialog.



You should see a set of scatter points appear at the location of the cell centroids. This scatter point set has a data set for the computed heads and for the top and bottom elevations of the model layers.

7 Approach to Building the Local Model Next, we will build the local model. There are numerous approaches to building the local model. A common approach is to mark the boundaries of the local model as specified head boundaries using the computed head values from the regional model. The following method accomplishes this objective:

A rectangular grid is constructed where two opposite boundaries are parallel to head contours from the regional model (i.e., a constant head value along each boundary). The other two boundaries are no flow boundaries and are perpendicular to the head contours from the regional model.

8 Building the Local Conceptual Model The simplest way to build the local model is to create a conceptual model in the Map module. To do this, we will create a new conceptual model.

1. If necessary expand the Map Data folder in the Project Explorer by clicking on the plus symbol next to the item.

2. Right-click on the Regional Model item and select the Duplicate command.

3. Change the name of the new conceptual model to to Local Model.

8.1 Creating a New Coverage Next, we will create a new source/sink coverage.

1. If necessary expand the Local Model item in the Project Explorer by clicking on the plus symbol next to the item.

2. Right-click on the ss coverage and select the Delete command from the menu.

3. Right-click on Local Model item in the Project Explorer and select the New Coverage command.

4. Change the name of the coverage to local ss.

5. In the Sources/Sinks/BCs spread sheet toggle on Layer Range and Specified Head (CHD).

6. Change the Default layer range to be 1 to 2.



7. Select the OK button.

Note that we did not delete the recharge and hydraulic conductivity coverages. We will use these coverages to construct our local model. The boundaries of the coverages are larger than they need to be but that does not matter.

8.2 Creating the Boundary Arcs Next, we will create the boundary arcs. First, we need to zoom in on the local site model:

8. Select the Zoom tool .

9. Drag a box around the local site boundary (the red rectangle).

10. Select the local ss coverage in the Project Explorer to make it the active coverage.

Create the boundaries as follows:

11. Select the Create Arc tool .

12. Create four arcs, two parallel to the contours, and two perpendicular to the contours as shown in Figure 2. Double click on the corners to end each arc.

Figure 2. Arcs to be created on boundary of local model.

8.3 Building the Polygon Next, we will use the arcs to build a polygon defining the model domain.



1. Select the Build Polygons button.

8.4 Marking the Specified Head Arcs The next step is to mark the specified head boundaries.

1. Select the Select Arcs tool .

2. While holding the Shift key, select the arcs on the left and right sides of the model.

3. Select Properties button .

4. In the All row of the spreadsheet change the type to spec. head (CHD). This will make both arcs specified head arcs.


At this point we need to select the nodes of the specified head arcs and assign a head value.

6. Select the Select Points/Nodes tool .

7. Select the two nodes on the left side of the model.

8. Select Properties button .

9. In the Head-Stage field enter a head value of 1050 for both nodes and hit the OK button.

10. Repeat this process for the two nodes on the right side of the model, but assign a head value of 1100.

9 Creating the Local MODFLOW Model We are now ready to convert the conceptual model to a grid model. First, we will create a new grid frame that fits the local model.

1. In the Project Explorer right-click on the empty space and then, from the pop-up menu, select the New | Grid Frame command.

2. Right-click on the Grid Frame in the Project Explorer and select the Fit to Active Coverage command from the pop-up menu.

3. If desired, you can use grid frame tool to position the grid frame to better match the local grid boundary.



9.1 Creating the Grid Next, we will create the grid.

1. In the Project Explorer right-click on the Grid Frame and select the Map To | 3D Grid command.

2. Select OK twice to confirm deletion of the existing grid and the MODFLOW data.

3. In the Create Finite Difference Grid dialog, enter 60 for the number of cells in the x direction, 50 for the number of cells in the y direction, and 2 for the number of cells in the z direction.

4. Select OK to create the grid.

You should see a grid appear. You can zoom in to examine the grid.

5. Select the Zoom tool .

6. Drag a box around the grid.

9.2 Activating the Cells Next, we will inactivate the exterior cells.


2. Select the MODFLOW | New Simulation command.

3. Select OK to accept the defaults in the MODFLOW Global / Basic Package dialog.

4. Select the Map Data folder in the Project Explorer.

5. Select the Feature Objects | Activate Cells in Coverage(s) command from the menu. If the arcs match the grid boundary closely, you may not see any cells inactivated. If, however, the grid extends significantly beyond the arcs, some cells will be inactivated.

9.3 Mapping the Properties Next, we will convert the MODFLOW data to the grid.

1. Right-click on the Local Model conceptual model in the Project Explorer and select the Map to | MODFLOW/MODPATH from the menu.

2. Select OK at the prompt to map All applicable coverages.



Note: At this point, our local scale model does not include the wells involved in the pump and treat system. These could be added at a later time.

10 Interpolating the Layer Data The final step in the conversion process is to interpolate the regional data from the scatter points to the MODFLOW layer arrays.

1. Right-click on the Regional Data Scatter set in the Project Explorer, and select the Interpolate To | MODFLOW Layers command.


Now that we’re done using the scatter points, lets turn them off to make it easier to see the grid.

3. Uncheck the box in the Project Explorer next to the 2D Scatter Data folder .

11 Saving and Running the Local Model We are now ready to save the MODFLOW model and run the simulation.


2. Select the File | Save As command.

3. Save the project with the name locmod.

To run MODFLOW:

4. Select the MODFLOW | Run MODFLOW command.

5. When the simulation is finished, select the Close button.

You should see a set of head contours that closely resemble the head contours from the regional model. At this point, the local flow model is complete and the injection and extraction wells could be added for the pump and treat simulations.

12 MODAEM Regional Model A regional MODAEM model can also be used to create a local MODFLOW model. For a more detailed description of MODAEM see the MODAEM tutorial. Instead of using a specified head boundary in the local ss coverage to assign heads to the MODFLOW model we will use a MODAEM head boundary. A MODAEM head boundary condition is linked to a MODAEM conceptual model. When the Map MODFLOW command is selected, the locations of all of the cells associated with the MODAEM head boundary are found. Then a MODAEM model runs in the background and computes the head at the



cell locations. Also, MODAEM computes the flow across the MODAEM head boundary. In summary, the MODAEM head boundary not only assigns heads to the MODFLOW model, but it also creates a flow observation.

12.1 Running MODAEM

Notice that there is now a Reg MODAEM conceptual model below the Map Data folder in the Project Explorer. We will now run the MODAEM model to see the head contours.

1. Expand the Reg MODAEM conceptual model in the Project Explorer by double-clicking on it.

2. Select the ss coverage to make it the active coverage.

3. Select the F5 key. This will run the MODAEM model for the Reg MODAEM conceptual model.

4. When MODAEM is finished, select the Close button on the MODAEM dialog.

You should now see the head contours from the Reg MODAEM conceptual model.

12.2 Adjusting the Coverage Setup

We will now change the local ss coverage of our Local Model conceptual model to use a MODAEM head boundary instead of a specified head boundary.

1. Select the local ss coverage in the Project Explorer to make it active.

2. Double-click on the local ss coverage to bring up the Coverage Setup dialog.

3. In the Sources/Sinks/BCs section toggle on MODAEM Head.

4. In the MODAEM models drop-down box, select Reg MODAEM.

5. Select OK to exit the dialog.

6. Choose the Select Arc tool and select the two specified head arcs.

7. Select the Properties button .

8. In the Type column of the All row, select MODAEM head as the type.

9. Select OK to exit the dialog.

12.3 Running the Local Model We are now ready to convert our local conceptual model to the 3D Grid.



1. Right-click on the Local Model conceptual model in the Project Explorer and select Map to | MODFLOW/MODPATH command from the pop-up menu.

2. Select OK at the prompt to use all applicable coverages.

3. Select the File | Save As command.

4. Save the project with the name locmod2.


6. Select the MODFLOW | Run MODFLOW command.

7. Select the Close button when MODFLOW is finished running.

You should see a set of head contours that are similar to the head contours from the regional model. The head contours from the regional MODAEM model are slightly different from the MODFLOW regional model so the sides of the local flow model that should represent parallel flow are most likely not perpendicular to the head contours from the MODAEM regional model. For this reason, the head contours do not match as well as they did for the conversion from the MODFLOW regional model.

13 Conclusion This concludes the Regional to Local Model Conversion tutorial. Here are the things that you should have learned in this tutorial:

• The Grid | MODFLOW Layers 2D Scatter Points command converts your MODFLOW elevation data into scatter points.

• The basic steps for doing Regional to Local model conversion in GMS are:

1. Generate the regional model and compute a solution.

2. Use the MODFLOW Layers 2D Scatter Points command to create the scatter point set with the layer and head data from the regional model.

3. Create the 3D grid for the local scale model.

4. Interpolate the heads and layer data values from the scatter points to the MODFLOW layer arrays for the local scale model.

• A local MODFLOW model can be constructed from a regional MODAEM model.


1 Contents2 Introduction2.1 Outline

3 Description of Problem4 Getting Started5 Reading in the Regional Model6 Converting the Layer Data to a Scatter Point Set7 Approach to Building the Local Model8 Building the Local Conceptual Model8.1 Creating a New Coverage8.2 Creating the Boundary Arcs8.3 Building the Polygon8.4 Marking the Specified Head Arcs

9 Creating the Local MODFLOW Model9.1 Creating the Grid9.2 Activating the Cells9.3 Mapping the Properties

10 Interpolating the Layer Data11 Saving and Running the Local Model12 MODAEM Regional Model12.1 Running MODAEM12.2 Adjusting the Coverage Setup12.3 Running the Local Model

13 Conclusion

gms 8.0 tutorial modflow – regional to local model...

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